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ObjectAbstractMap
InternalConcurrentHashMap
public class InternalConcurrentHashMap
A hash table supporting full concurrency of retrievals and
adjustable expected concurrency for updates. This class obeys the
same functional specification as Hashtable
, and
includes versions of methods corresponding to each method of
Hashtable. However, even though all operations are
thread-safe, retrieval operations do not entail locking,
and there is not any support for locking the entire table
in a way that prevents all access. This class is fully
interoperable with Hashtable in programs that rely on its
thread safety but not on its synchronization details.
Retrieval operations (including get) generally do not
block, so may overlap with update operations (including
put and remove). Retrievals reflect the results
of the most recently completed update operations holding
upon their onset. For aggregate operations such as putAll
and clear, concurrent retrievals may reflect insertion or
removal of only some entries. Similarly, Iterators and
Enumerations return elements reflecting the state of the hash table
at some point at or since the creation of the iterator/enumeration.
They do not throw
ConcurrentModificationException
. However, iterators are
designed to be used by only one thread at a time.
The allowed concurrency among update operations is guided by the optional concurrencyLevel constructor argument (default 16), which is used as a hint for internal sizing. The table is internally partitioned to try to permit the indicated number of concurrent updates without contention. Because placement in hash tables is essentially random, the actual concurrency will vary. Ideally, you should choose a value to accommodate as many threads as will ever concurrently modify the table. Using a significantly higher value than you need can waste space and time, and a significantly lower value can lead to thread contention. But overestimates and underestimates within an order of magnitude do not usually have much noticeable impact. A value of one is appropriate when it is known that only one thread will modify and all others will only read. Also, resizing this or any other kind of hash table is a relatively slow operation, so, when possible, it is a good idea to provide estimates of expected table sizes in constructors.
This class and its views and iterators implement all of the
optional methods of the Map
and Iterator
interfaces.
Like Hashtable
but unlike HashMap
, this class does NOT allow null to be
used as a key or value.
This class is a member of the Java Collections Framework.
Nested Class Summary |
---|
Nested classes/interfaces inherited from interface Map |
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Map.Entry<K,V> |
Constructor Summary | |
---|---|
InternalConcurrentHashMap()
Creates a new, empty map with a default initial capacity (16), load factor (0.75f), and concurrencyLevel (16). |
|
InternalConcurrentHashMap(int initialCapacity)
capacity, and with default load factor (0.75f) and concurrencyLevel (16). |
|
InternalConcurrentHashMap(int initialCapacity,
float loadFactor)
Creates a new, empty map with the specified initial Creates a new, empty map with the specified initial capacity and load factor and with the default concurrencyLevel (16). |
|
InternalConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel)
Creates a new, empty map with the specified initial capacity and the specified load factor. |
|
InternalConcurrentHashMap(Map t)
Creates a new map with the same mappings as the given map. |
Method Summary | |
---|---|
void |
clear()
Removes all mappings from this map. |
boolean |
contains(Object value)
Legacy method testing if some key maps into the specified value in this table. |
boolean |
containsKey(Object key)
Tests if the specified object is a key in this table. |
boolean |
containsValue(Object value)
Returns true if this map maps one or more keys to the specified value. |
Enumeration |
elements()
Returns an enumeration of the values in this table. |
Set |
entrySet()
Returns a collection view of the mappings contained in this map. |
Object |
get(Object key)
Returns the value to which the specified key is mapped in this table. |
boolean |
isEmpty()
|
Enumeration |
keys()
Returns an enumeration of the keys in this table. |
Set |
keySet()
Returns a set view of the keys contained in this map. |
Object |
put(Object key,
Object value)
Maps the specified key to the specified value in this table. |
void |
putAll(Map t)
Copies all of the mappings from the specified map to this one. |
Object |
putIfAbsent(Object key,
Object value)
If the specified key is not already associated with a value, associate it with the given value. |
Object |
remove(Object key)
Removes the key (and its corresponding value) from this table. |
boolean |
remove(Object key,
Object value)
Remove entry for key only if currently mapped to given value. |
Object |
replace(Object key,
Object value)
Replace entry for key only if currently mapped to some value. |
boolean |
replace(Object key,
Object oldValue,
Object newValue)
Replace entry for key only if currently mapped to given value. |
int |
size()
|
Collection |
values()
Returns a collection view of the values contained in this map. |
Methods inherited from class AbstractMap |
---|
clone, equals, hashCode, toString |
Methods inherited from class Object |
---|
finalize, getClass, notify, notifyAll, wait, wait, wait |
Methods inherited from interface Map |
---|
equals, hashCode |
Constructor Detail |
---|
public InternalConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel)
initialCapacity
- the initial capacity. The implementation
performs internal sizing to accommodate this many elements.loadFactor
- the load factor threshold, used to control resizing.concurrencyLevel
- the estimated number of concurrently
updating threads. The implementation performs internal sizing
to try to accommodate this many threads.
IllegalArgumentException
- if the initial capacity is
negative or the load factor or concurrencyLevel are
nonpositive.public InternalConcurrentHashMap(int initialCapacity, float loadFactor)
initialCapacity
- The implementation performs internal
sizing to accommodate this many elements.loadFactor
- the load factor threshold, used to control resizing.
IllegalArgumentException
- if the initial capacity of
elements is negative or the load factor is nonpositivepublic InternalConcurrentHashMap(int initialCapacity)
initialCapacity
- The implementation performs internal
sizing to accommodate this many elements.
IllegalArgumentException
- if the initial capacity of
elements is negative.public InternalConcurrentHashMap()
public InternalConcurrentHashMap(Map t)
t
- the mapMethod Detail |
---|
public boolean isEmpty()
isEmpty
in interface Map
isEmpty
in class AbstractMap
public int size()
size
in interface Map
size
in class AbstractMap
public Object get(Object key)
get
in interface Map
get
in class AbstractMap
key
- a key in the table.
NullPointerException
- if the key is
null.public boolean containsKey(Object key)
containsKey
in interface Map
containsKey
in class AbstractMap
key
- possible key.
NullPointerException
- if the key is
null.public boolean containsValue(Object value)
containsValue
in interface Map
containsValue
in class AbstractMap
value
- value whose presence in this map is to be tested.
NullPointerException
- if the value is null.public boolean contains(Object value)
containsValue(java.lang.Object)
, and exists solely to ensure
full compatibility with class Hashtable
,
which supported this method prior to introduction of the
Java Collections framework.
value
- a value to search for.
NullPointerException
- if the value is null.public Object put(Object key, Object value)
The value can be retrieved by calling the get method with a key that is equal to the original key.
put
in interface Map
put
in class AbstractMap
key
- the table key.value
- the value.
NullPointerException
- if the key or value is
null.public Object putIfAbsent(Object key, Object value)
if (!map.containsKey(key)) return map.put(key, value); else return map.get(key);Except that the action is performed atomically.
key
- key with which the specified value is to be associated.value
- value to be associated with the specified key.
NullPointerException
- if the specified key or value is
null.public void putAll(Map t)
putAll
in interface Map
putAll
in class AbstractMap
t
- Mappings to be stored in this map.public Object remove(Object key)
remove
in interface Map
remove
in class AbstractMap
key
- the key that needs to be removed.
NullPointerException
- if the key is
null.public boolean remove(Object key, Object value)
if (map.get(key).equals(value)) { map.remove(key); return true; } else return false;except that the action is performed atomically.
key
- key with which the specified value is associated.value
- value associated with the specified key.
NullPointerException
- if the specified key is
null.public boolean replace(Object key, Object oldValue, Object newValue)
if (map.get(key).equals(oldValue)) { map.put(key, newValue); return true; } else return false;except that the action is performed atomically.
key
- key with which the specified value is associated.oldValue
- value expected to be associated with the specified key.newValue
- value to be associated with the specified key.
NullPointerException
- if the specified key or values are
null.public Object replace(Object key, Object value)
if ((map.containsKey(key)) { return map.put(key, value); } else return null;except that the action is performed atomically.
key
- key with which the specified value is associated.value
- value to be associated with the specified key.
NullPointerException
- if the specified key or value is
null.public void clear()
clear
in interface Map
clear
in class AbstractMap
public Set keySet()
ConcurrentModificationException
,
and guarantees to traverse elements as they existed upon
construction of the iterator, and may (but is not guaranteed to)
reflect any modifications subsequent to construction.
keySet
in interface Map
keySet
in class AbstractMap
public Collection values()
ConcurrentModificationException
,
and guarantees to traverse elements as they existed upon
construction of the iterator, and may (but is not guaranteed to)
reflect any modifications subsequent to construction.
values
in interface Map
values
in class AbstractMap
public Set entrySet()
ConcurrentModificationException
,
and guarantees to traverse elements as they existed upon
construction of the iterator, and may (but is not guaranteed to)
reflect any modifications subsequent to construction.
entrySet
in interface Map
entrySet
in class AbstractMap
public Enumeration keys()
keySet
public Enumeration elements()
values
|
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